Carriers and service providers query an ENUM infrastructure to translate telephone numbers, such as E.164 numbers, into Uniform Resource Identifiers (URIs). Each URI is used to complete a respective Voice over Internet Protocol (VoIP) call to its associated telephone number.
The Public ENUM infrastructure comprises of Tier-0, Tier-1 and Tier-2 databases. The Tier-0 database is indexed by country codes and points queries to an appropriate Tier-1 database. The Tier-0 database is operated by RIPE in Europe. The Tier-1 databases are to point queries to an appropriate Tier-2 database. The Tier-1 databases are to be operated by individual countries. In Country Code 1, the function of Tier-1 is subdivided into Tier-1a and Tier-1b. Tier-1a, which is indexed by NPA, points queries to an appropriate Tier-1b, which is indexed by full E.164. Each country may operate its own Tier-1b. Tier-1b points queries to the Tier-2 having actual records of services associated with each of a plurality of telephone numbers.